Liquid metering devices which utilize a rotating member having a cavity or cavities of known volume have been devised wherein the flow is measured by counting the number of times each cavity is filled and emptied. Representative of this approach is U.S. Pat. to Stitzel No. 297,092 in which filling and emptying of the cavity is effected through use of a piston. U.S. Pat. to Porterfield No. 3,200,643 also discloses a metering device in which compartments are alternately filled and emptied and, since the capacity of each compartment is known, determination of quantity of liquid passing through the meter is determined by counting the number of revolutions of the drum.
Special problems are inherent in the measuring of the volume rate of flow of milk produced during the milking operations, since the rate of flow will vary greatly with each animal and particularly at lower rates of flow, close accurate measurement through utilization of commercially available systems has been difficult at best. For instance U.S. Pat. to Olander No. 3,783,837 is directed to a system for regulating the amount of vacuum or negative pressure employed in a milk receiver in response to the rate of milk flow. U.S. Pat. to Needham No. 3,733,016 is directed to a system for detecting the flow of milk in an automated milking machine in such a way as not to permit teat cup removal in the event of a temporary interruption in flow.
Another problem associated with milk volume metering devices is to establish close correlation between the operation of the metering unit and other sensing and monitoring operations to be conducted during the milking operation, such as, temperature sensing, feed control, fluid conductivity sensing which is specifically useful in the detection of bovine mastitis and the controlled application of vacuum to the metering device during removal of the teat cups at the conclusion of the milking operation so as to minimize the possibility of injury to the udder while avoiding premature removal in the event of temporary interruptions in milk flow.
It is therefore highly desirable to provide for a liquid metering apparatus which is extremely accurate and capable of operating at flow rates down to as low as 0 lbs. per minute but which is not affected by vacuum or pressure fluctuations and will not cause fluctuations to occur. Another desirable feature is that the metering device be capable of being cleaned automatically in place at the conclusion of each milking operation in a rapid efficient manner, is low in cost, and does not require special milk filtration. Still further, the metering device should minimize the formation of bubbles or foam as the milk enters and flows through the metering apparatus.